How to test strong params with Rspec?

Question

What is the actual strategy to test strong params filtering in Rails controller with Rspec? (Except shoulda matchers) How to write failing test and then make it green?

Answer 1

Create 2 hashes with expected and all (with unsatisfied) parameters. Then pass all params to action and check that you object model receiving only expected params. It will not if you are not using strong parameter filters. Than add permissions to params and check test again.

For example, this:

# action
def create
  User.create(params)
end

# spec
it 'creates a user' do
  expect_any_instance_of(User).to receive(:create).
    with({name: 'Sideshow Bob'}.with_indifferent_access)
  post :create, user: 
    { first_name: 'Sideshow', last_name: 'Bob', name: 'Sideshow Bob' }
end

will pass all params to User and test will fail. And when you filter them:

def user_params
  params.require(:user).permit(:name)
end

and change action with User.create(user_params), test will pass.

Answer 2

Here is how I did it:

  describe 'Safe Params' do

   let(:mixed_params) {
     {
       blueprint_application_environment: {
         id: 1000,
         blueprint_id:   1,
         application_id: 2,
         environment_id: 3
       },
       format: :json
     }
   }

context "when processing a Post request with a mix of permitted and unpermitted parameters" do
   before { post :create, mixed_params }

  it "a create will not set the value of the unpermitted parameter" do
     expect(JSON.parse(response.body)["id"]).not_to eq(1000)
   end

  it "a create will set the value of the permitted parameters" do
     expect(JSON.parse(response.body)["blueprint_id"]).to eq(1)
     expect(JSON.parse(response.body)["application_id"]).to eq(2)
     expect(JSON.parse(response.body)["environment_id"]).to eq(3)
   end
 end

end

Controller code:

  def create
    @blueprint_application_environment = BlueprintApplicationEnvironment.new(blueprint_application_environment_params)
    if @blueprint_application_environment.save
      render 'show.json.jbuilder'
    else
      render json: @blueprint_application_environment.errors, status: :unprocessable_entity
    end
  end

def blueprint_application_environment_params
    params.require(:blueprint_application_environment).permit(:blueprint_id, :application_id, :environment_id)
end